New York City health officials are investigating a cluster of Legionnaires’ disease in the Carnegie Hill and Yorkville neighborhoods, with 23 confirmed cases and 17 hospitalizations as of July 6 and no reported deaths. The likely source is one or more cooling towers in ZIP codes 10028, 10128, and 10075, and officials are testing all such towers in the area. Legionnaires’ disease is a pneumonia caused by Legionella bacteria that grow in warm water and spread through building water systems.